Automobile Audio System

ABSTRACT

The invention features a dual-mode audio system for an automobile which in one mode is configured for play while the doors to the automobile are closed, and in a second mode, is configured for play while a door, such as a tailgate, is opened. Additionally, the invention also features a battery monitor which monitors the operating condition of the battery and may estimate the energy capacity of the battery. The system may also take power conservation measures if the system determines that the engine is not running or the operating condition of the batter reaches a predetermined state. The invention also features a remote control integrated within a key fob for controlling the audio system. The invention features various orientations for mounting a pair of loudspeakers within an automobile which directly radiate sound out of a rear opening of the automobile.

TECHNICAL FIELD

This invention relates to audio systems, and more particularly to audiosystems for automobiles.

BACKGROUND

Audio systems are included in virtually every automobile manufacturedtoday. These audio systems are typically designed for use while thedoors, tailgates, and other openings to the passenger compartment areclosed. However, people often choose to listen to their automobile audiosystem while they are outside of their vehicle, such as while they arecamping or “tailgating” at a sporting event. Because traditionalautomobile audio systems are not designed for this type of use,listeners may not enjoy as high a quality sound presentation as theycould if the system were designed for outdoor use.

The acoustic characteristics of a typical vehicle with all of its doorsclosed will generally be significantly different than the acousticcharacteristics of the same vehicle with its tailgate (or one of itsdoors) open. For example, the linear transfer function from each speakerelement to various listening locations will be markedly different ineach circumstance. Furthermore, opening or closing of the tailgatesignificantly alters the acoustic characteristics of the cabin space.

Accordingly, it is desirable to have an automobile audio system which isable to operate in two modes: one mode where one or more parameters ofthe audio system are configured to better optimize sound quality whilethe doors (to include tailgates) are closed and a second mode where oneor more parameters of the audio system are configured to better optimizesound quality while one or more of the doors, such as a tailgate, areopen.

Additionally, users may wish to operate their automobile audio systemwhile the engine is not running and thus drain power from theautomobile's battery. It is therefore desirable for an automobile audiosystem to monitor one or more operating conditions of the battery andadjust system performance in order to extend the maximum period of timethe audio system can operate from battery power. It is also desirable tomonitor one or more operating conditions of the battery to ensureoperation of the audio system does not result in a condition wheresufficient battery charge (to allow the automobile to be restarted) isno longer available.

It should be noted that the terms automobile and vehicle are usedsynonymously in this description and refer to any self-propelledpassenger vehicle used for land transport, including cars, trucks,pick-up trucks, sport utility vehicles, and the like. Additionally, theterm tailgate refers to a hinged door of an automobile which providesaccess to a rear opening of the automobile. A tailgate may be hingedlyconnected to the top, bottom, or side of the frame of the automobile.

SUMMARY

According to an aspect of the invention, a system and method foroperating an audio system in an automobile includes implementing a firstsystem configuration, receiving an input indicating a change inoperating mode, and in response to this input, implementing a secondsystem configuration which is different from the first systemconfiguration, wherein the second system configuration is implementedwhen one of the doors, such as a tailgate, of the automobile is open.

Embodiments include one or more of the following features. The firstsystem configuration may occur when all of the doors of the automobileare closed and the second configuration may occur when one or more ofthe doors, such as a tailgate, are opened.

The audio system may implement a different system topology in the firstand second system configurations, where the system topology defines howdifferent signals provided by an audio source are routed to thedifferent speakers of the audio system.

The audio system may implement different signal processing operation inthe first and second system configurations. The different signalprocessing operations in the first and second system configurations mayinclude different equalization signal processing operations,amplification operations, dynamic range control operation, or spatialenhancement operations.

The audio system may also receive input indicating that the automobile'sengine is not running, and, in response to this input, the first orsecond system configuration may be adjusted in order to reduce powerconsumption of the system. Several adjustments may be made to the firstor second system configuration to reduce power consumption includingturning off one or more speakers (e.g., by muting the output of theamplifier, placing the amplifier in standby mode, reducing the voltageof the audio signal input to the amplifier to approximately zero,disconnecting the one or more loudspeakers from the amplifier, removingelectrical power from the amplifier); reducing the gain in one or moreof the signal paths; controlling the maximum output power level of theaudio system (e.g., by dynamically adjusting the gain of a variable gainelement as a function of a detected level of an audio signal); orchanging one or more other signal processing operations in the first orsecond system configuration.

The audio system may switch between the first and second systemconfiguration by monitoring one or more physical conditions of theautomobile (e.g., whether a door is opened, the engine is running, or anoccupant is in the automobile) and generate a switch command based on achange in one or more of the monitored physical conditions. The audiosystem may provide a manual switch accessible to a user and changebetween system configurations based on the state of the switch. Themanual switch may be located on a remote control device (e.g., a keyfob) or mounted at one or more locations within the automobile (e.g., ona front or rear control panel).

The audio system may also include a battery monitoring process whichreceives input indicating one or more operating conditions of thebattery (e.g., the battery voltage, discharge current, temperature). Thebattery monitoring process may compare one or more of the monitoredoperating conditions to a predetermined state, and if the monitoredoperating conditions reach the predetermined state, then the systemwould take a responsive action such as triggering an alarm or reducingthe power consumption of the audio system. The battery monitoringprocess may further estimate the remaining capacity of the battery basedon one or more of the monitored operating conditions and compare theestimated capacity to a predetermined value, and, if the estimatedcapacity reaches or falls below the predetermined value, then the systemmay take a response action such as triggering an alarm or reducing thepower consumption of the audio system.

In another aspect, the invention features a method for remotelycontrolling an audio system in an automobile with a key fob having aplurality of buttons which includes defining a first set of commandscorresponding to each button on the key fob, wherein the first set ofcommand includes a command to actuate the door locks. The method alsoincludes defining a second set of commands corresponding to each button,wherein the second set of commands includes one or more commands forcontrolling the audio system of the automobile. The method furtherincludes switching between the first and second sets of commands basedon a predetermined condition.

Embodiments may include one or more of the following features. The keyfob may include a switch having two states, and the predeterminedcondition is a state of the switch. The audio system may have a firstmode of operation and a second mode of operation and the predeterminedcondition is the state of the mode of operation of the audio system,such that the first set of commands are valid when the audio system isin the first mode of operation and the second set of commands are validwhen the audio system is in the second mode of operation.

In another aspect, the invention features a system and method foroperating an audio system in a vehicle with a battery that includesmonitoring one or more operating conditions of the battery, comparingone or more of the monitored conditions of the battery to apredetermined state, if the monitored operating conditions of thebattery reaches the predetermined state, then triggering an alarm.

Embodiments may include one or more of the following features. The alarmmay be an audible alarm, visual alarm, or tactile alarm. One or more ofthe monitored operating conditions of the battery may include sensingthe output voltage level of the battery, sensing the discharge currentof the battery; or sensing the ambient temperature.

In another aspect the invention features a system and method foroperating an audio system in a vehicle with a battery that includesmonitoring one or more operating conditions of the battery, comparingone or more of the monitored conditions of the battery to apredetermined state, and if the monitored operating conditions of thebattery reaches the predetermined state, then causing the automobile tostart its engine.

In another aspect, the invention features a system and method foroperating an audio system in a vehicle with a battery that includesmonitoring one or more operating conditions of the battery, comparingone or more of the monitored conditions of the battery to apredetermined state, and if the monitored operating conditions of thebattery reaches the predetermined state, then turning off a subset ofthe plurality of speakers.

In another aspect, the invention features a system and method foroperating an audio system in a vehicle with a battery that includesmonitoring one or more operating conditions of the battery, comparingone or more of the monitored conditions of the battery to apredetermined state and if the monitored operating conditions of thebattery reaches the predetermined state, then adjusting one or more ofequalization signal processes to change the frequency response of theaudio system.

In another aspect, the invention features a system and method foroperating an audio system that includes monitoring one or more operatingconditions of the battery, comparing one or more of the monitoredconditions of the battery to a predetermined state, and if the monitoredoperating conditions of the battery reaches the predetermined state,then detecting the level of one or more of audio signals received froman audio source, and dynamically adjusting the gain of one or morevariable gain elements as a function of the level of one or more audiosignals received from an audio source.

In another aspect, the invention features a system and method foroperating an audio system that includes monitoring one or more operatingconditions of the battery, estimating the remaining capacity of thebattery based on one or more of the monitored operating conditions ofthe battery, comparing the estimated remaining capacity of the batteryto a predetermined value; and, if the estimated remaining capacity ofthe battery is equal to or less than a predetermined value, then causingthe audio system to take an action.

Embodiments may include one or more of the following features. Theaction taken by the audio system in response to reaching or fallingbelow the predetermined value may include triggering an alarm, causingthe automobile to start the engine, or reducing the power consumption ofthe audio system (e.g., by turning off one or more loudspeakers, turningoff the system, adjusting one or more equalization processes applied toone or more audio signals to change the frequency response of the audiosystem).

In another aspect, a system and method for operating an audio system inan automobile includes determining whether the engine is running, and,in response to the system determining that the engine is not running,then changing one or more signal processes to reduce power consumptionof the audio system.

Embodiments may include one or more of the following features. Thesystem may reduce power consumption in various ways including by turningoff one or more speakers, adjusting one or more of the equalizationprocesses performed on one or more of the received audio signals tochange the frequency response of the audio system, reducing the gain inone or more of the audio signal paths.

In another aspect, an audio system for an automobile includes an audioinput source, a plurality of loudspeakers, a first set of operatingconditions for a first mode of operation, a second set of operatingconditions for a second mode of operation, wherein the second set ofoperating conditions is different from the first set of operatingconditions and occurs when one of the doors of the automobile is open,and a switch for changing between the first and second set of operatingconditions.

Embodiments may include one or more of the following features. The firstset of operating conditions are configured for play while a tailgate isclosed and listeners are within the automobile and the second set ofoperating conditions are configured for play while a tailgate is openand listeners are outside the automobile. The audio system may alsoinclude at least one channel of equalization, wherein the first set ofoperating conditions defines a first frequency response of the channelof equalization and the second set of operating conditions defines asecond frequency response of the channel of equalization. The audiosystem may also include a dynamic range control device configured toreceive an audio signal having a first dynamic range and output an audiosignal having a second dynamic range, wherein the second dynamic rangeis different than the first dynamic range. The system may also include abattery monitoring process.

The audio system may also include a rear control panel located withinthe passenger compartment of the automobile towards the back of theautomobile that includes one or more controls for operating the audiosystem. The rear control panel may include a switch for changing betweenthe first and second set of operating conditions. The rear control panelmay also include at least one pair of external audio source line levelinputs, an external microphone level input, or a separate video outputjack for connection to a video display.

In another aspect, the invention features an audio system for anautomobile having a passenger compartment and a tailgate hingedlyconnected to the top portion of the automobile's frame that includes afirst speaker set having a first speaker and a second speaker. The firstand second speakers are mounted on the tailgate of the automobile suchthat each speaker directs sound along a primary axis of radiation andhas a fixed orientation such that each speaker's primary axis ofradiation directs sound substantially towards the passenger compartmentof the automobile when the tailgate is closed, and the speaker's primaryaxis of radiation is pointed away from the passenger compartment of theautomobile and is angled relative to the plane of the ground when thetailgate is opened.

Embodiments may include one or more of the following features. Thespeakers may be mounted near an upper edge of the tailgate, for example,on the window of the tailgate.

The audio system may be have a first mode of operation configured forplay while the tailgate is closed and listeners are within theautomobile and a second mode of operation configured for play while thetailgate is opened and listeners are outside the automobile near therear of the automobile. The audio system may also have a second set ofspeakers that includes a first and second speaker, and mounted such thateach speaker having primary axis of radiation that is pointedsubstantially towards the rear of the automobile and which direct soundoutside the automobile in the second mode of operation.

In another aspect, an audio system for an automobile having a passengercompartment and a tailgate hingedly connected to the automobile's frameand a rear seat or seats having a front portion and a rear portionincludes first speaker set that includes a first speaker and a secondspeaker. The first speaker set is mounted on the rear portion of therear seat or seats, such that each speaker in the first set of speakersdirects sound along a primary axis of radiation and has a fixedorientation such that each speaker's primary axis of radiation directssound substantially away from the passenger compartment of theautomobile towards the tailgate when the tailgate is closed, and thespeaker's primary axis of radiation is pointed away from the passengercompartment of the automobile and directs sound out of the rear of theautomobile when the tailgate is opened.

In another aspect, an audio system for an automobile having a rear seat,a passenger compartment with a floor, and a tailgate hingedly connectedto the automobile's frame includes a first speaker set comprising afirst speaker and a second speaker. The first speaker set is mounted onthe floor, wherein each speaker in the first set of speakers directssound along a primary axis of radiation and has a fixed orientation suchthat each speaker's primary axis of radiation directs soundsubstantially away from the passenger compartment of the automobiletowards the tailgate when the tailgate is closed, and the speaker'sprimary axis of radiation is pointed away from the passenger compartmentof the automobile and directs sound out of the rear of the automobilewhen the tailgate is opened.

In another aspect, an audio system for an automobile having a rear seat,a passenger compartment with a ceiling, and a tailgate hingedlyconnected to the automobile's frame includes a first speaker setcomprising a first speaker and a second speaker. The first speaker setis mounted on the ceiling, wherein each speaker in the first set ofspeakers directs sound along a primary axis of radiation and has a fixedorientation such that each speaker's primary axis of radiation directssound substantially away from the passenger compartment of theautomobile towards the tailgate when the tailgate is closed, and thespeaker's primary axis of radiation is pointed away from the passengercompartment of the automobile and directs sound out of the rear of theautomobile when the tailgate is opened.

In another aspect, an audio system for an automobile having a passengercompartment with a ceiling, floor, and sidewalls, and having a rearopening includes a first speaker set comprising a first speaker and asecond speaker. The first speaker set is mounted within the passengercompartment in the rear half of the automobile (e.g., on the floor orceiling), wherein each speaker in the first set of speakers directssound along a primary axis of radiation and has a fixed orientation suchthat each speaker's primary axis of radiation direct sound substantiallytowards the rear opening of the automobile and wherein the neitherspeaker in the first speaker set is mounted on a sidewall of thepassenger compartment.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a is a top view of an automobile having a dual-mode audiosystem.

FIG. 1B is a top view of an automobile having another dual mode audiosystem.

FIG. 2A is a flow-chart illustrating the operation of a mode detectionprocess in a dual-mode audio system.

FIG. 2B is a flow-chart illustrating the operation of a mode detectionprocess in a tri-mode audio system.

FIG. 3 is a flow-chart illustrating the operation of a batterymonitoring process in a dual-mode audio system.

FIG. 4 is a diagram of a sport utility vehicle having a rear set ofcontrols and rear speakers mounted on its tailgate.

FIGS. 5A-5D are side views of an automobile having rear speakers mountedin four different locations.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

As shown in FIG. 1A, an automobile (e.g., an SUV) 10 includes an audiosystem 20 that is configured to operate in two modes: a conventionalmode and an open mode.

The conventional mode is a mode of operation in which audio system 20 isconfigured for play when all of the doors of the vehicle are closed andthe primary listening position of interest is the seating area withinthe passenger compartment. In this mode, sound is radiated within thepassenger compartment as in a conventional automobile audio system.

The open mode is a mode of operation in which audio system 20 isconfigured for play when the tailgate 11 is open. In this mode, sound isradiated through the open tailgate and/or through the vehicle's bodypanels or other openings to the outside environment. The primarylistening position of interest in this case is outside of the vehicle,typically in line with the open tailgate 11. In other embodiments, theopen mode of operation may be configured for play when one or more doors(including a tailgate) are open.

Because the acoustic characteristics of the vehicle are significantlydifferent when all of the doors are closed versus when one or more doorsare opened, and because the listening positions of primary concern aredifferent in the different modes, the audio system 20 adjusts systemconfiguration in order to better optimize performance in each mode. Aswill be explained in greater detail below, adjustment of systemconfiguration may include altering the system topology for each mode ofoperation, as well as performing different signal processing operationssuch as equalization, signal mixing, amplification, dynamic rangecontrol, spatial enhancement processes and other signal processingtechniques on the channels of audio data in each mode of operation. Thesystem topology defines how different signals provided by an audiosource are routed to the different speakers of the audio system.

Additionally, audio system 20 features a battery monitoring processwhich monitors one or more operating conditions of the automobilebattery 30 and takes one or more actions based on whether the system 20is primarily running off of the battery and the state of one or more ofthe monitored operating conditions. As will be explained in greaterdetail below, the battery monitoring process takes various actionsincluding triggering an alarm and altering the system configuration inorder to conserve battery power.

Referring again to FIG. 1A, audio system 20 includes one or more audiosources (not shown) such as a stereo radio, CD player, DVD player,and/or an MP3 player, which may be mounted in or near a front controlconsole 21, a rear control console 22, or at another location within theautomobile 10. The front and rear control consoles 21, 22 each maycontain a set of controls (e.g., volume, source selection, trackselection, play, pause, etc.) for the audio sources included within thesystem 20.

Audio system 20 also includes two pair of front speakers 24 a-24 b, 24c-24 d, a pair of side speakers 26 a-26 b, a pair of rear speakers 28a-28 b, and a woofer 29.

It should be noted that the arrangement of elements, as well as thenumber of elements shown in FIG. 1A, were chosen to illustrate the novelfeatures of the invention. It should be understood that the invention isnot limited to use of the particular configuration of speaker elementsand placements shown. For example, as shown in FIG. 1B, anotherdual-mode audio system 20′ may include a front center speaker 25′located in the dashboard of the automobile 10′ and a rear center speaker23′ located near the rear of the passenger's compartment in the vehicle.

FIGS. 2A and 3 illustrate operation of the audio system 20 shown in FIG.1A.

As shown in FIG. 2A, the audio system 20 includes a mode detectionprocess 100 which detects when the system 20 is turned on 102 and when aswitching event 108, 114 occurs. A switching event occurs when a userchanges the state of a switch provided within the system 20. One or moremanual switches may be located on the front control panel 21 (shown inFIG. 1A), rear control panel 22, on a remote control device, on a keyfob, or in another location. Since it is possible that significantchanges would be made in system operation when the mode is changed,having a manual switch keeps from dramatically changing system operationwhile passengers remain inside the vehicle.

In other embodiments, a switching event may occur automatically. Forexample, a switching event may occur automatically when the systemdetects that a tailgate or door is open and the vehicle engine is notrunning (which can be sensed by the state of the ignition interlock, theRPM of the engine, or some other means). It may also be desirable tosense if passengers remain in the vehicle cabin, which could be doneusing seat switches, ultrasonic motion detectors, or some other method.Thus, in other embodiments, the system may automatically switch modes tothe open mode when the tailgate or door is open, the engine is off, andno passengers are occupying the vehicle cabin.

Referring again to FIG. 2A, when the mode detection process 100 detectsthat the system 20 has been turned on 102, the process 100 will placethe system in a conventional mode of operation 104. By automaticallyreverting to a conventional mode when the system is turned on, thesystem avoids a situation where the driver gets into the vehicle andturns on the system after it had been switched to open mode. However, inother embodiments, a mode detection process in a dual-mode audio systemcould be configured to start up in different modes depending on how thesystem was turned on or the state of a switch. For example, if thesystem was turned on using controls mounted in the front of the vehicle,the system may assume that someone would be inside the vehicle and thesystem should start in conventional mode. If the system were turned onusing controls that were easily accessible from outside the vehicle(such as controls located in rear console 22, or controls located on aremote control), the system may be configured to start up in open mode.

When the system 20 is placed in the conventional mode of operation 104,the system 20 is in a first system configuration 106 which, as will beexplained in more detail below, has a first system topology and performsa first set of signal processing operations which are configured forplay with the doors of the vehicle closed and the primary listeningposition within the passenger's compartment. The system 20 remains inits first system configuration 106 until a switching event is detected108.

If a switching event is detected 108, mode detection process 100 placesthe system in the open mode of operation 110 and the system 20 ischanged over to a second system configuration 112 which has a secondsystem topology and performs a second set signal processing operationsthat is configured for play with the tailgate of the vehicle opened andthe primarily listening position outside of the vehicle, near the rearopening.

If another switching event 114 is detected, then the mode detectionprocess 100 reverts the system 20 back to the conventional mode ofoperation 104 and the system is placed in the first system configuration106.

In each system configuration, 106, 112, the system 20 has a certainsystem topology which defines how different signals provided by an audiosource are routed to the various speakers in the system. In the firstsystem configuration 106, the system topology is arranged in order tobetter optimize the system for play with the doors of the automobileclosed and the primary listening in the seating area in the passengercompartment. Similarly, in the second system configuration 112, thesystem topology is arranged in order to better optimize the system forplay with a rear tailgate opened and the primary listening positionoutside the automobile near the rear opening. For example, in an audiosystem 20 having a speaker configuration similar to the arrangement inFIG. 1A and an audio source which produces 5.1 channels of audio data(i.e., front left, front right, front center, left surround, and rightsurround of full bandwidth (20-20 kHz) audio data plus a sixth channelof low frequency audio data), the first and second system configuration106, 112 may have a system topology as shown in Table I.

TABLE I System Topology in Conventional Mode (i.e., speakers (shown inFIG. System Topology in Open Mode (i.e., 1A) which receive audio data inthe speakers (shown in FIG. 1A) which Audio Data Conventional mode)receive audio data in the Open mode) Front left audio data Front leftspeakers 24b, 24d Rear left speaker 28b Front right audio data Frontright speakers 24a, 24c Rear right speaker 28a Front center dataProvided equally to front left and right Provided equally to rear leftand rear speakers 24a-24d right speakers 28a-28b Left Surround audiodata Side left speaker 26b and rear left Side left speaker 26b and frontleft speaker 28b speakers 24a, 24d Right Surround audio Side rightspeaker 26a and rear right Side right speakers 26a and front right dataspeaker 28a speakers 24a, 24c Low Frequency data (i.e., Subwooferspeaker 29 Subwoofer speaker 29 the .1 channel)In other separate embodiments, many other speaker arrangements androuting of audio data is possible. For example, an audio system may havea speaker arrangement as shown in FIG. 1B and may have an audio sourcewhich produces 6.1 channels of audio data including a front left, frontright, front center, left surround, right surround, and center surroundof full bandwidth (20-20 kHz) of audio data plus a sixth channel of lowfrequency audio data. In this example, the system configuration 106, 112may have the system topology as shown in Table II.

TABLE II System Topology in Conventional Mode (i.e., speakers (shown inFIG. System Topology in Open Mode (i.e., 1B) which receive audio data inthe speakers (shown in FIG. 1B) which Audio Data Conventional mode)receive audio data in the Open mode) Front left audio data Front leftspeakers 24b, 24d Rear left speaker 28b Front right audio data Frontright speakers 24a, 24c Rear right speaker 28a Front center data Frontcenter speaker 25 Rear center speaker 23 Left Surround audio data Sideleft speaker 26b and rear left Side left speaker 26b and front leftspeaker 28b speakers 24a, 24d Right Surround audio Side right speaker26a and rear right Side right speakers 26a and front right data speaker28a speakers 24a, 24c Center Surround audio Center rear speaker 23Center front speaker 25 data Low Frequency data (i.e., Subwoofer speaker29 Subwoofer speaker 29 the .1 channel)

In other embodiments, a system configuration may include a topology inwhich one or more speakers are shut off in different modes of operation.For example, referring again to FIG. 1A, the front left and rightspeakers 24 a-24 d may be shut off in the open mode of play leaving theside speakers to output left and right surround sound. Alternatively,the side speakers may be shut off in the open mode, leaving the frontspeakers to output the left and right surround sound. Similarly, therear speakers 28 a-28 b may be shut off in the conventional mode leavingthe side speakers to output the surround sound.

Other embodiments may shut off front speakers 24 a-24 d (shown inFIG. 1) and side speakers 26 a-26 b in open mode. In this arrangement,left, right and center surround signals would be mixed with the left,right and center front signals that are fed to speakers 28 a-28 b.

In addition to changing the system topology in each mode of operation,the first and second system configuration 106, 112 also performdifferent signal processing operations in each mode. Signal processingoperations may include operations such as equalization, amplification,signal mixing, spatial enhancement, dynamic range control and othersignal processing techniques on one or more channels of audio data inorder to alter the frequency response (both magnitude and phase as afunction of frequency), polarity, and the magnitude of the voltage levelof the signals delivered to each of the speaker channels in each themode of operation.

The first and second system configurations 106, 112, may performdifferent equalization signal processing operations in order to providefor a different frequency response of the system 20 in each mode ofoperation. Equalization signal processing may be performed using any ofthe various techniques known in the art. For example, equalizationsignal processing may be performed on each channel of audio data bypassing the data through one or more digital filters whose filtercoefficients are stored in memory and provided to the digital signalprocessor. Sets of filter coefficients corresponding to each mode ofoperation would be stored in memory, and the system could switch sets ofcoefficients according to commands issued by the mode detection process100.

Equalization processing operations may also be implemented in the analogdomain by providing physically separate circuits with separate sets offilters for each mode of operation. Different circuits would be switchedinto or out of the signal path in accordance with commands issued by themode control process 100. Alternatively, there may be one physicalcircuit in which the performance can be dynamically adjusted through useof variable gain circuits, voltage controlled filters, switchableelectrical component values, switched capacitor filters, or any otherform of adjustable or programmable analog filters or signal processors.

Equalization signal processing operations, whether implemented in thedigital or analog domain, should be designed to provide a smootherfrequency response of the audio system in each mode of play as comparedto the frequency response of the system with no equalization.Furthermore, the frequency response of the system measured at thedesired listening position for the open mode of operation (outside ofthe vehicle in line with the open door or tailgate) should be smootherusing the signal processing designed for operation in the open mode thanthe response would be if the conventional mode signal processing wereused. For each mode of operation, the overall measured frequencyresponse of the system measured at each desired listening position willgenerally be similar in character. However, the frequency response ofthe signal processing used for each mode will generally be significantlydifferent. For purposes of discussion, it should be noted that we willsometimes refer to signal processing used for equalization as a ‘channelof equalization’ in this specification. The channel of equalization maybe accomplished using either analog or digital techniques. We will alsosometimes refer to the frequency response of the signal processing asthe ‘frequency response of the channel of equalization’.

First and second system configurations 106, 112, may include differentamplification processing operations of the audio signals applied to aspeaker for each mode of operation. In other words, the first systemconfiguration 106 may include signal processing operations which adjustthe amplification of the audio signals in one manner, and the secondsystem configuration may include signal processing operations whichadjust the amplification of the audio signals in a different manner.Adjusting the amplification of the audio signals may be performed usingany of the techniques known in the art. Adjusting gain can be done inmultiple places within the signal path of an audio signal, and thesystem is not limited in the locations where gain adjustment occurs. Forexample, the amplification of an audio signal applied to a speaker maybe adjusted by changing the gain of an amplifier in the signal path of aparticular speaker. In a digital system, the gain for each channel foreach mode of operation may be determined by a multiplication coefficientor set of filter coefficients stored in memory and supplied to a digitalsignal processor in order to control the level of the signal supplied toone or more speakers in each mode of operation. The gain may also beadjusted in the analog domain by controlling a variable gain analogamplifier (or other known methods of controlling gain in an analogsystem) located in the signal path of each channel of audio data.

The first and second system configurations 106, 112 may performdifferent signal mixing signal processing functions in each mode ofoperation. Signal mixing operations involve summing various signalstogether is various proportions. Mixing may occur in one or both modesof operation. Summing can be accomplished using op amp summer circuitryin the analog domain, or data values can be directly summed by amicroprocessor or digital signal processor.

The first and second system configuration 106, 112 may include differentspatial enhancement signal processing in each mode of operation. Spatialenhancement signal processing generally improves the spatial characterof the sound field created by the system and may be implemented usingany of the techniques known in the art. One spatial enhancementtechnique for two-channel audio involves determining first sum anddifference signals by alternately adding and subtracting first andsecond signals from each other (hereinafter referred to as a matrixoperation). Next, some form of signal processing is applied at least tothe difference signal (or possibly to both the sum and differencesignals, where the processing applied to the sum and difference signalsis different), then a second matrix operation (take sum and differenceof processed sum and difference signals) is performed to generate thirdand fourth signals. These third and fourth signals are now spatiallyenhanced versions of the first and second signals. Other enhancementtechniques might only operate on a difference signal. In these methods,a difference of two signals is taken. The difference signal is modifiedin some manner, then added back to one of the original channels andsubtracted from the other of the original channels.

In the open mode of operation, spatial enhancement may be performed onthe signals provided to the rear speakers (e.g., speakers 28 a-28 b inFIG. 1A) since these speakers will most likely be the primary speakersproviding sound to listeners. Spatial enhancement may be performed onthe complete signals applied to the rear speakers, or may be applied toonly a portion of the signals applied to the rear speakers. For example,for reproduction of a surround sound signal source, center channelinformation may be applied to each rear speaker equally, without anyspatial enhancement processing. Simultaneously, left and right channelsignals may be applied to left and right speakers respectively. Thesecould be applied with or without spatial enhancement processing.Similarly, left and right surround signals could be applied with orwithout spatial enhancement processing to left and right speakersrespectively, where the spatial enhancement processing used could eitherbe the same as or different from that applied to the left and rightchannel signals. In one particular embodiment, the second configurationfeeds center channel signals equally to rear speakers 28 a-28 b (shownin FIG. 1A) without spatial enhancement, front left and right signals toleft and right rear speakers 28 a-28 b respectively without spatialenhancement, and spatially enhanced left and right surround signals toleft and right rear speakers 28 a-28 b respectively.

Other combinations of performing spatial enhancement processing ofvarious signals is also possible. For example, a system such as thatdescribed in co-pending application titled “Audio Signal Processing”having U.S. Ser. No. 09/886,868 filed on Jun. 21, 2001 and assigned toBose® Corporation, which is herein incorporated by reference, could beused in the rear of the vehicle, where spatial enhancement processing isused with the configuration of speakers disclosed.

It should be understood that spatial enhancement is not limited to thesecond system configuration during the open mode of operation, but mayalso be performed on the audio signals provided to one or more sets ofspeakers (e.g., the front sets of speakers 24 a-24 b, 24 c-24 d or rearsets of speakers 26 a-b, 28 a-b shown in FIG. 1A) in first systemconfiguration during the conventional mode of operation.

It should be noted that other signal processing operations which affectsystem functions or performance attributes may change in theconventional and open mode of operation. For example, the dynamic rangeof the audio signal supplied to one or more speakers may be changeddepending on the mode of operation. Additionally, balance/fade settingsmay be changed depending on the operation (e.g., fade control may beshut off or set to some fixed position in the open mode).

Equalization processes, amplification, spatial enhancement, signalmixing, dynamic range adjustment, and other signal processes may takeplace in either the digital domain with a device such as digital signalprocessor, microprocessor, digital amplifier, or other suitable digitaldevice, or in the analog domain with separate physical circuits or asingle physical circuit with dynamically adjustable elements (e.g.,variable gain amplifiers, voltage controlled filters, etc.).

Additionally, while a dual-mode audio system is illustrated in FIG. 2A,the concept may be extended to audio systems which operate in three ormore modes of operation. For example, as shown in FIG. 2B, an audiosystem may have a first system configuration 154 (with a first topologyand a first set of signal processing operations) in a conventional modewhen all of the doors of the automobile are closed, a second systemconfiguration 162 (with a second topology and second set of signalprocessing operations) when one set of doors (e.g., a tailgate only) areopen, and a third system configuration 168 (with a third topology and athird set signal processing operations) when a different set of doors(e.g., a tailgate and a rear door) are open. When a switching eventoccurs 156, 164, 170, mode detection process 150 determines the propermode of operation 152, 160, 166 based on the state of a switch and/orthe state of one or more physical conditions of the automobile (e.g.,whether doors are opened/closed, engine is off/running, passenger in/outof driver's seat, etc.) and modifies the audio data accordingly.

As shown in FIG. 3, audio system 20 also may include a batterymonitoring process 200 which may receive input 202 from the automobile10 that indicates whether the engine of the automobile is running, whichtells the audio system whether the primary power supply is theautomobile's battery or another power source such as an alternator.Numerous possible signals could be provided to indicate whether or notthe engine is running, such as a tachometer signal indicating the RPM ofthe engine (i.e., if RPM is zero, then the engine is not running andpower is being drawn primarily from the battery), a signal indicatingthe state of the ignition lock (i.e., if the ignition is locked then theautomobile is not running), or any of a number of digital signals thatmay be available on a communications bus which may be included in avehicle electrical system.

If the battery condition monitoring process 200 detects that the engineis running 203 (and thus power is not being primarily drawn from thebattery), then there is no adjustment to the system configuration inorder to conserve battery power 204.

When the battery condition monitoring process 200 detects that theengine is not running 203 (and thus power is being primarily drawn fromthe battery), the system 20 may adjust system configuration (i.e.,system topology, signal processing operations or both) to conservebattery power 206 using a variety of techniques without substantiallydegrading system performance. For example, since the front speakers(e.g., 24 a-b, 24 c-24 d in FIG. 1A) consume power but do notappreciably affect system performance outside the rear of the vehicle,the system may be configured to shut off the front pair speakers whenoperating under battery power in open mode. Similarly, the rear speakers(28 a-28 b in FIG. 1A) may be shut off when operating in theconventional mode. Thus, it should be understood that the adjustment tosignal processes to conserve power 206 may differ depending on the modeof operation of the audio system 20. By adjusting system configurationin order to conserve power when the battery monitoring process detectsthat the engine is not running, the system is able to extend the lengthof time it may operate under battery power.

Speakers may be shut off in a variety of ways, including by muting theoutput of the amplifier feeding a particular speaker, placing theamplifier in a standby mode (many commercially-available amplifierintegrated circuits, such as the TDA 8567Q amplifier manufactured byPhilips® Semiconductor, are configured with both mute and standbymodes), reducing the audio signal fed into an amplifier to substantiallyzero, interrupting the signal path between an amplifier and a speaker,or removing power from an amplifier feeding a particular circuit orspeaker.

Since a significant amount of power is concentrated in the low frequencyportion of music, the system may the raise cutoff frequencies (orincrease the order of attenuation as a function of frequency, or both)of high pass filters that may be located in the signal path of one ormore of the signals delivered to the speakers in order to conservepower.

Power may also be conserved by reducing the magnitude of the voltage ofthe audio signal applied to one or more speakers. One technique forreducing the magnitude of the voltage is to reduce the gain in thesignal path of the audio signal (which can be done by changing the gainof an amplifier, or the attenuation of a passive attenuator in analogimplementations, or by changing coefficients in digital filters ordigital multiplication operations in digital systems). Another techniquefor reducing the magnitude of the voltage of audio signals is throughthe use of a dynamic range control device in the signal path of theaudio signal. A dynamic range control device is a device which limits,compresses, expands or otherwise changes the dynamic range of an audiosignal.

One use of dynamic range control devices in audio systems is to keep adevice (typically a power amplifier) from clipping its output A dynamicrange control device used in this type of application is commonly knownas a limiter and is configured to keep the maximum voltage applied tothe amplifier below a set minimum value under all operating conditions.

Dynamic range control devices are typically constructed using a variablegain element (such as an amplifier in an analog implementation or amultiplier in a digital implementation), a control element, and a signaldetector of some type (typically a level detector to detect, peak,average or RMS level of a signal, although other types of detectors arealso possible), where the gain of the variable gain element is varied assome function of the detected signal of interest by the control element.The function defines the relationship between the gain of the variablegain element and the detected quantity of the signal of interest. Thenature of the function may change depending on the detected quantity, ormay remain constant over the entire range of detected values. Forexample, a threshold value for the detected quantity may be determined,where the gain of the variable gain element is not changed as long asthe detected quantity remains below the threshold value, but the gain ischanged according to the specified function if the detected quantityexceeds the threshold level. Limiters work by reducing the gain of thevariable gain element when the sensed parameter of the signal exceedssome set threshold value, which is usually chosen to allow maximumoutput of a device (such as a power amplifier) without clipping. Thus,in one embodiment the battery monitoring process may reduce the maximumvoltage of an audio signal applied to one or more speakers by loweringthe threshold value of a limiter when the battery monitoring process 200detects that the audio system 20 is primarily running off of thebattery.

Referring again to FIG. 3, the battery condition monitoring process 200receives input 208 about various operating conditions of the battery andestimates the approximate amount of energy remaining in the battery, inorder to ensure that there is sufficient charge remaining in the batteryto re-start the automobile. If the estimated battery capacity reaches orfalls below a predetermined threshold value, then the system 20 maynotify the user that battery energy is getting low 210 and may takefurther power conservations measures 212.

The battery condition monitoring process 200 receives input 208indicating various factors related to the current operating condition ofthe battery. These conditions may include the discharge currentmagnitude and rate, the accumulated time discharging has been occurring,the ambient temperature, battery output voltage, and other conditionsthat one skilled in the art might wish to monitor in order to estimatethe remaining capacity of the battery. From these conditions, process200 estimates the remaining capacity of the battery.

The voltage profile of a battery is the relationship between the batteryoutput voltage and the discharge conditions (length of time the batteryhas been discharging, rate of discharge, magnitude of discharge current,temperature). The output voltage of a secondary (re-chargeable) batterydecreases over time according the discharge conditions. Batteries, likelead-acid batteries commonly used in automobiles, do not have a singulardischarge curve over all operating temperatures and discharge currents.Rather, a particular battery's voltage profile curve is a function ofthe operating conditions described above. The set of battery voltageprofile curves for a particular battery are readily available from themanufacturer. Manufacturers also provide curves showing battery capacityas a function of operating conditions. One technique for estimating theremaining capacity of the battery involves determining where the batteryis operating on its appropriate discharge (profile) curve, given the(monitored) operating conditions. From this information and the capacityinformation available from the manufacturer, the remaining batterycapacity can be estimated.

Another technique for estimating the remaining capacity of the batteryis to estimate the state of charge of the battery by measuring how muchenergy is put into it during charging and how much energy is drainedfrom it when it is in use. This is sometimes called coulomb counting. Ina separate embodiment, a battery monitoring process may monitor theamount of current being discharged from the battery as well as theamount of current that charges the battery and, from these measurements,estimate the remaining charge in the battery.

When the estimated capacity reaches a predetermined value above theminimum level necessary for normal re-starting of the vehicle (which isset as the battery capacity threshold value), the battery conditionmonitoring process 200 will inform the user 210 by issuing an alarm,which can be audible (e.g., output through the audio system) or visual(e.g., on a visual display) or tactile (e.g., actuate a vibrating devicesuch as a pager). In other separate embodiments, the battery conditionmonitoring process 200 may shut down the audio system or place thesystem in a standby (or sleep) mode in which all unnecessary components,including all amplifiers, are shut off when the estimated capacityreaches the battery capacity threshold value. Also, in a vehicleequipped with remote starting capability, a battery condition monitoringprocess may trigger the remote starting process to periodically startthe vehicle to recharge the battery when the estimated capacity reachesthe battery capacity threshold value.

In other separate embodiments, a battery condition monitoring processmay have several predetermined thresholds which cause the system to takedifferent power conservation measures (e.g., shutting off speakers,adjusting equalization, automatically starting the automobile, reducingthe magnitude of voltage of the audio signals applied to a speaker,placing the system in a standby mode, shutting off the system etc.) atdifferent predetermined holds.

In another embodiment, an audio system may include a battery monitoringprocess which does not estimate the remaining capacity of the bay, butwhich monitors one or more operating conditions of the battery such asthe discharge current, current drawn by the audio system, temperature,or the battery's voltage. The battery monitoring process which monitorsthe operating condition of the battery may take one or more actions,such as triggering an alarm, reducing power consumption, placing thesystem in a standby mode, or completely shutting down the system, if theoperating condition of the battery reaches a predetermined state. Thepredetermined state may be the state of one or more of the monitoredconditions such as the battery voltage, discharge current, and ambienttemperature, or a combination of conditions.

It should be noted that any number of the known techniques forestimating the remaining capacity of a battery or monitoring theoperating condition of a battery may be utilized in other embodimentsand the invention is not limited to the particular embodiments describedabove.

In other separate embodiments, an audio system may raise the cut-offfrequencies of the high pass filters, shut off speakers, limit the gainof the amplifiers, reduce the dynamic range of audio signals, or takeother energy conservation measures either whenever operation on batterypower is detected (as shown in FIG. 2A), or when remaining batteryenergy decreases to a predetermined threshold. It should be understoodthat a battery monitoring process may be implemented in a dual modeaudio system (as in audio system 20 shown in FIG. 1A-1B) or in a purelyconventional audio system.

The circuitry implementing the mode selection, battery conditionmonitoring processes, and system configurations 100, 200, 106, 112, 206,210, 212 illustrated in FIG. 2-3 may be implemented in hardware,software, firmware or the like in one or more locations in the audiosystem 20. For example, the circuitry for all of the processes may bephysically located in the front control console 21 or rear controlconsole 22 (in FIG. 1A) or the circuitry may be distributed acrossseveral devices of the system.

In a conventional vehicle audio system, the audio sources are typicallylocated in front of the vehicle or at least a control interface for theaudio sources is located in the front. When the audio system isoperating in the open mode, for convenience, the audio sources or atleast a set of controls for the audio sources should be accessible fromthe open tailgate (or door), which would normally be at the rear of thevehicle where the listeners would be located. As shown in FIG. 4, aduplicate set of user controls 80 is provided within the vehicle 10cabin near the opening of the rear tailgate 50. This may be a completeset of duplicate controls, such as source selection, volume, and sourcetransport controls (e.g., play, stop, pause, skip forward, skipbackwards, fast forward, fast reverse, preset selection, tune up ordown, etc.). Alternatively, the rear console may be some subset of thecomplete control interface present in the front of the vehicle.Additionally, FIG. 4 shows a set of speakers 64 mounted on the vehicle'stailgate 50 such that their primary axis of radiation 70 is directed atan angle of approximately 45 degrees relative to the plane of the groundon which the vehicle sits when the tailgate 50 is opened, and theprimary axis of radiation 70 substantially faces into the passengercompartment of the vehicle when the tailgate is closed.

An additional way of controlling the audio sources from the rear of thevehicle is to implement the control functions using a remote control. Aseparate remote control may be used, or audio system control functionscould be integrated onto a vehicle key fob remote, similar to those forremote keyless entry. Using a key fob remote, a plurality of buttons canbe added to the key fob to provide limited audio function controls suchas volume and source selection. Alternatively, existing key fob remotebuttons that operate normal functions such as lock and unlock with thevehicle operating in conventional mode, can be re-mapped to operateaudio functions when the vehicle is operating in open mode. Re-mappingcould occur by activating a switch, button, or a sequence of buttons tochange the remote function from normal vehicle functions to audio systemfunctions. For example, one method to do this is by adding a shiftbutton that changes the functions of other buttons on the remote.Alternatively, the vehicle could sense the mode, and change itsinterpretation of the commands sent by the key fob remote. For example,lock and unlock could become volume up and down when the system wasoperating in open mode.

Additionally, one or more external audio system inputs may be providedin the rear of the vehicle. For example, one input may be optimized toaccept the output of a microphone. In this case, additionalpre-amplification (and possibly a separate volume control) may berequired. This would allow the vehicle to be used as a portable publicaddress system. A line level input may also be provided. This wouldallow additional sources, such as a portable MP3 or CD player, to beconnected to the system and be easily accessible from the rear.

Other features may be included in a rear control panel. For example,when the vehicle is equipped with an integrated video source (DVD-video,VHS, etc), a video output jack can be made accessible from the rear ofthe vehicle, so a video display may be attached.

FIGS. 5A-5D illustrate several locations where rear speakers may bemounted in order to provide high quality sound for both modes ofoperation. It should be noted that the speakers illustrated in FIGS.5A-5D may be upper frequency speakers (e.g., tweeters, mid-ranges), ormay be substantially full range speakers (which radiate sound over themajority of the audible frequency range of the human auditory system).Additionally, although speakers 60, 62, 64, and 66 shown in FIGS. 5A,5B, 5C, and 5D, respectively, are shown as individual transducers, itshould be understood that the speakers may also be mounted withinenclosures.

The primary axis of radiation of a speaker is the direction in which thespeaker radiates maximum energy over the majority of its operatingrange. This direction is typically in line with physical center axis ofsymmetry of an axi-symmetric transducer. For ease of understanding,axi-symmetric transducers are assumed to be used here, and the axis ofprimary radiation is assumed to be aligned with the center axis ofsymmetry of the transducer and points away from the front surface of theprimary radiating surface of the transducer, where the front surface isthe surface that is coupled to the listening environment. It should benoted, however, that the invention is not limited to use ofaxi-symmetric transducers. The orientations described can be adjusted asneeded such that sound radiation is directed in the desired directions.

As shown in FIG. 5A, an automobile 10 includes a rear tailgate 50 havingan upper hinge 51 which is shown as open. A pair of rear speakers 60(e.g., mid-range speakers) are mounted within the automobile cabin nearthe opening of the tailgate 50 such that the pair of speakers 60 areoutwardly directed from the cabin when the tailgate 50 is opened. Whenthe tailgate 50 is closed, sound from speaker pair 60 is reflected offof the tailgate back into the automobile cabin. There are numerouslocations in the rear portion of the cabin of the automobile wherespeakers 60 may be mounted and the invention is not limited to thespecific location illustrated in FIG. 5A. Additionally the speaker pair60 may be oriented such that they do not point directly at the tailgate50 when the tailgate is closed, but may be angled with respect to thetailgate 50. For example, in separate embodiments, speaker pair 60 maybe mounted on the cabin floor, cabin ceiling, cabin sidewalls, rearcabin deck, or back of the rearmost seat in the automobile 10. Finally,an additional speaker, such as a subwoofer may also be mounted withinthe passenger compartment near the tailgate.

FIGS. 5B-5C illustrate additional separate embodiments of where pairs ofrear speakers may be mounted on an automobile 10 having a tailgate 50.Specifically, FIG. 5B shows a pair of rear speakers 62 mounted withinthe automobile cabin near the top hinge 51 of the tailgate 50.

FIG. 5C shows a pair of rear speakers 64 mounted on the tailgate 50 suchthat the left speaker is located in the upper left-hand side of thetailgate and a right speaker is located in the upper right-hand side ofthe tailgate. The speakers 64 may be mounted within the trim of thetailgate 50. The speakers may also be mounted on a window on thetailgate 50 using methods similar to those used to attach a rear viewmirror to a front windshield. The window mounted speakers mayadditionally be attached to the trim surrounding the window foradditional structural support. The pair of rear speakers 64 are alsooriented such that the primary axis of radiation 70 of the speakers 64face substantially towards the rear of the automobile 10 and are angledat an angle of approximately 45 degrees relative to a plane parallel tothe ground when the tailgate is open. Similarly, the primary axis ofradiation 70 of the speakers 64 is pointed substantially towards thepassenger cabin when the tailgate is closed. This speaker orientationmay be particularly advantageous because it directs sound into thevehicle when the tailgate is closed and also outwardly directs soundfrom the vehicle when the tailgate is open. Thus, this speakerorientation is particularly well-suited for accommodating both modes ofoperation of the audio system.

FIG. 5D shows another pair of rear speakers 66 mounted on the tailgate50 roughly midway between the upper hinge 51 and lower edge 52 of thetailgate 50. While this speaker orientation is well-suited for operationin the conventional mode of operation because sound is directed into thepassenger cabin when the tailgate is closed, this orientation may not beoptimal for listeners that are located behind the automobile 10, awayfrom the tailgate, as these listeners will be significantly off-axis tothe main axis of radiation of the speakers 66.

While FIGS. 5A-5D illustrate various locations of a single pair of rearspeakers, additional separate embodiments may include audio systemswhere multiple pairs of rear speakers are mounted at multiple locationsin automobile cabin and tailgate. Additionally, note that speakers 60,62, 64, and 66 shown in FIGS. 5A, 5B, 5C and 5D, respectively, representa pair of speakers symmetrically located within the automobile, wherethe axis of symmetry is the centerline of the automobile 10.

A number of embodiments have been described, however, it is evident thatthose skilled in the art may make numerous modifications of thedepartures from the specific apparatus and techniques disclosed hereinwithout departing from the inventive concepts. Consequently, theinvention is to be construed as embracing each and every novel featureand novel combination of features present in or possessed by theapparatus and techniques disclosed herein and limited solely by thespirit and scope of the appended claims.

1-109. (canceled)
 110. An audio system for an automobile having apassenger compartment with a ceiling, floor, and sidewalls, and having arear opening comprising: a first speaker set comprising a first speakerand a second speaker mounted within the passenger compartment in therear half of the automobile, wherein each speaker in the first set ofspeakers direct sound along a primary axis of radiation and have a fixedorientation such that each speaker's primary axis of radiation directsound substantially towards rear opening of the automobile and whereinthe neither speaker in the first speaker set is mounted on a sidewall ofthe passenger compartment.
 111. The audio system of claim 110 whereinthe first set of speakers is mounted on the ceiling within the passengercompartment.
 112. The audio system of claim 110 wherein the first set ofspeakers is mounted on the floor within the passenger compartment